A disk drive system includes one or more magnetic recording disks and control mechanisms for storing data on the disks. The trend in the design of magnetic hard disk drives is to increase the recording density of a disk drive system. Recording density is a measure of the amount of data that may be stored in a given area of a disk. Achieving higher areal density (i.e., the number of stored bits per unit surface area) requires that the data tracks be closer to each other. Also, as the track widths are made smaller, misregistration of a track more often affect the writing and/or reading with the head by an adjacent track. This behavior is commonly referred to as adjacent track interference (ATI). One method for addressing ATI is to pattern the surface of the disk to form discrete data tracks, referred to as discrete track recording (DTR).
Conventional DTR structures have been described, for example, by Morita in U.S. Pat. No. 6,088,200 and Mundt et al. in U.S. Pat. No. 6,563,673. FIG. 1 depicts a conventional DTR structure 100 utilizing a pattern of concentric discrete magnetic regions 111 and 112 as the recording medium. The discrete magnetic regions 111 and 112 are disposed on areas of a non-magnetic substrate 105. The substrate surface areas 105 not containing the magnetic material separate the discrete magnetic regions 111 and 112 from one another by the cross-track or radial width, Strough, to form concentric data tracks having a track pitch, Ptrack, in the user data area 110. As shown, the track pitch, Ptrack, is the sum of the cross-track width of the discrete magnetic region 112 and the cross-track width of the separation between the adjacent discrete magnetic region 111. Thus, the track pitch, Ptrack, is a useful dimension for characterizing the concentric physical data track pattern of a particular DTR disk.
The cross-track width is typically less than the width of the recording head such that, during operation, portions of the head extend over the non-magnetic regions 105, which may be implemented as spaces, troughs, valleys, grooves, etc., as the head flies over the disk on an air bearing sufficiently close to a discrete magnetic region, which may be implemented as hills, elevations, etc., to enable the writing of data in a particular track. Therefore, with DTR, data tracks are defined both physically and magnetically.
Because a head must fly over a particular track in the down-track direction during operation, it is important to accurately measure the position of the head periodically. FIG. 1 further depicts a conventional means for making such a determination by physically defining a non-user data area 101, in the DTR media. The non-user data area 101 typically includes timing, address alignment and other control information used by the disk drive system. Thus, the non-user data area 101 will generally include a timing line pattern comprising lands, such as the timing land 120, a gray code pattern comprising lands, such as the gray code land 125 and a servo pattern comprising lands, such as the servo land 130. Each of timing land 120, gray code land 125 and servo land 130 is physically defined with a relative alignment to the data tracks in the user data area 110. As shown, surrounding each of the timing land 120, gray code land 125 and servo land 130, is the non-magnetic trough 105.
However, conventional control sector patterns, such as those shown in the non-user data area 101, have a number of shortcomings. First, the very large cross-track width of troughs and lands is problematic for the electron beam patterning techniques typically employed at least once in the fabrication process, usually for the patterning of a master disk. As shown, each of the timing land 120, gray code land 125 and servo land 130 have a cross-track width at least as great as the track pitch, Ptrack and may be many times the track pitch, Ptrack. Conventionally, an electron beam “writes” on regions that are precursors to regions of a non-magnetic substrate 105. During such writing, an electron beam having a dimension Strough defines the space between data tracks to have the dimension, Strough. However, because the dimension of the electron beam, Strough, is generally fixed during the writing process, patterning the much larger cross-track widths of the non-magnetic substrate 105 surrounding the timing land 120, gray code land 125 and servo land 130, the electron beam with the Strough dimension requires “stitching” together a plurality of electron beam pixel patterns written individually. This stitching process can cause significant patterning errors when each individual pattern is not perfectly aligned with another. This type of patterning error can degraded the function of the timing land 120, gray code land 125 and servo land 130. Furthermore, writing one pixel at a time to such a relatively large area can significantly affect the total time required to form a pre-formatting pattern.
The conventional patterns depicted in FIG. 1 may also be difficult to physically define in a magnetic media with an imprinting operation. Conventional imprinting operations typically must compress a material located in the non-magnetic region 105. Such compression generally requires a pattern providing a pathway for compressed material to extrude. As shown in FIG. 1, because of the large cross-track width of the timing land 120 and gray code land 125, the non-magnetic region 105 between these two lands has no such pathway. Thus, the conventional patterns disadvantageously hinder the imprinting process.
The difference in pattern density between the servo area 101 and the user data area 110 is yet another disadvantage of conventional patterns. Pattern density transitions between regions can disadvantageously cause perturbations in the head as it flies between the regions during operation of the disk drive system. As shown in FIG. 1, the user data area 110 has a consistent pattern density defined by the track pitch, Ptrack, while the non-user data area 101 has much less consistency and includes patterns having a cross-track width much larger than Ptrack. These characteristics may perturb the flight of a disk drive slider. Conventional non-user data patterns however, are limited to controlling only the down-track or circumferential lengths of the lands and troughs to mitigate the effects of pattern density variation on a slider.